List to object[]

Question

I have a method that returns a List<string> and I'm trying to pass that to the AddRange(Object[]) method of a ComboBox.

How can I convert my List<string> to Object[]?

I suppose I could do a foreach but I'd rather use the AddRange(Object[]) as it's faster (and produces less code).

EDIT

The following works fine:

var list = new List<string>();
object[] array = list.ToArray<object>();
comboBox.AddRange(array);

However, on another note, any reason why I would want to perform the above instead of:

var list = new list<string>();
comboBox.AddRange(list.ToArray<object>());

MarcinJuraszek · Accepted Answer · 2018-05-12T06:01:53.827

15

You can do it using ToArray generic method:

var list = new List<string>();
object[] array = list.ToArray<object>();

You don't even need Cast<object>, because ToArray takes IEnumerable<T> which is covariant on generic type parameter.

edited May 12 '18 at 06:01

answered Sep 05 '13 at 10:19

MarcinJuraszek

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2

Arrays are also covariant, so you don't even need to do `list.ToArray – Magnus Grindal Bakken Sep 05 '13 at 10:21
2

@MagnusGrindalBakken: Well, it depends on whether the OP may want to store non-strings in the same array later. – Jon Skeet Sep 05 '13 at 10:23
@MagnusGrindalBakken You can take advantage of that, when calling methods like `AddRange`, but otherwise when you'd like to use that array later I would suggest using `ToArray – MarcinJuraszek Sep 05 '13 at 10:24
2

@MagnusGrindalBakken just doing `list.ToArray()` produces a warning saying `Co-variant array conversion from string[] to object[] can cause run-time exception on write operation`. – cogumel0 Sep 05 '13 at 10:26
@cogumel0 The warning you're quoting is the same Jon Skeet pointed few comments above. – MarcinJuraszek Sep 05 '13 at 10:27
@cogumel0 I think that's a Resharper warning. (I don't use Resharper so I've never seen it.) It's certainly a good idea to steer clear of array covariance in general, although it shouldn't be an issue in this case if all you're doing is `comboBox.Items.AddRange(myList.ToArray());`. I won't discourage you from working around the warning. – Magnus Grindal Bakken Sep 05 '13 at 10:35

score 4 · Answer 2 · answered Sep 05 '13 at 10:17

4

You can use something like to be explicit about the change of the type:

object[] array = yourList.Cast<Object>().ToArray();

or simply be implicit:

yourcomboBox.AddRange(yourList.ToArray());

answered Sep 05 '13 at 10:17

sloth

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score 1 · Answer 3 · answered Sep 05 '13 at 10:18

1

List<string> items = ...;
cb.Items.AddRange(items.ToArray());

answered Sep 05 '13 at 10:18

FireShock

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The only solution here that doesn't forget that arrays are covariant already in C#. – Sebastian Redl Sep 05 '13 at 10:21
1

This produces `Co-variant array conversion from string[] to object[] can cause run-time exception on write operation`, which is why I deviated from it. – cogumel0 Sep 05 '13 at 10:23

score 1 · Answer 4 · answered Sep 05 '13 at 10:18

1

Maybe this works:

object[] myArray = myList.OfType<object>().ToArray();

answered Sep 05 '13 at 10:18

BendEg

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score 0 · Answer 5 · answered Sep 05 '13 at 10:22

Arrays of references are covariant (slowly covariant) with arrays of their base classes (and with arrays of their interfaces, and with other arrays), so you can:

AddRange(mystrings.ToArray());

mystrings.ToArray() is a string[], that is covariant with an object[] (so that the AddRange will accept it)

From 12.5 Array covariance

For any two reference-types A and B, if an implicit reference conversion (Section 6.1.4) or explicit reference conversion (Section 6.2.3) exists from A to B, then the same reference conversion also exists from the array type A[R] to the array type B[R]

score 0 · Answer 6 · answered Sep 05 '13 at 10:28

If it's about convenience:

public static class ObjectCollectionExtension
{
    public static void AddAll<T>(this ComboBox.ObjectCollection self, IEnumerable<T> es)
    {
        foreach (var e in es)
            self.Add(e);
    }
}

Might have gotten the generics wrong, I'm a bit rusty.

List to object[]

6 Answers6